1. Field of the Invention
The present invention relates to a process, in particular a mask-free one-step process, for localized functionalization of conductive or semiconductive portions of composite surfaces with organic coatings, or alternatively to a process of mask-free localized organic grafting onto conductive or semiconductive portions of composite surfaces.
2. Discussion of the Background
There are at the present time four means identified for producing this type of localized organic grafting:                (i) Electronic or photochemical addressing with radiation1.        (ii) Electrovaporization with masking2.        (iii) Mechanical addressing by micropipetting and automatic distribution3.        (iv) Two-dimensional electrophoretic addressing4.        (v) The microcontact printing technique5.        
The point that processes (i) to (v) have in common is that they can be broken down into:                a paving, certain areas of which it is desired to cover with an organic coating;        a method for triggering the manufacture of chemical bonds between the organic molecules and the surface. This involves, respectively: (i) a beam of particles (photons, electrons or ions); (ii) to (v) chemisorption or physisorption reactions;        a “masking” process, responsible for the localization, which makes it possible to govern the fact that the triggering method will act on one given area of the paving and not on another. This involves, respectively: (i) focussing the beam; (ii) a physical mask; (iii) mechanical positioning of a tip or a nozzle; (iv) the two-dimensional protocol for placing under potential; (v) resolution of the etching on the ink pad and of the “flash” of the fluids printed on this etching.        
In all these processes, only the masking phase is responsible for the localization obtained. In particular, this phase is independent of the topology of the paving that it is desired to dress: specifically, assuming that it is the same paving that it is desired to cover in places by these various processes: added to the complexity of manufacturing the paving is the complexity of the localization (or “masking”) process, which usually requires a complex development and apparatus. Neither the agent triggering the chemical reaction for surface functionalization nor the localization offered by the paving before intervention participate in the efficacy of the localization: in process (i), the triggering agent is the beam of particles (photons, electrons or ions), optionally guided by a mask (see, in this respect, document U.S. Pat. No. 3,271,180 (1966)); in process (ii), the triggering agent (non-localized) is polarization of the substrate on which react molecules spatially filtered by a mask: the mask ensures the localization; in process (iii), the triggering factor is again polarization of the substrate, and the localization arises from the fact that the molecules are deposited by micropipetting at the bottom of a small trough etched into the substrate, and made conductive by depositing gold; in process (iv), the molecules are guided by gel electrophoresis to the desired area, and then fixed via a chemical reaction in the gel (using a reagent which constitutes the triggering agent).
In all these processes, the spatial resolution of the grafting is thus that of the “masking” process: it does not exploit to the maximum the geometrical guide already offered by the paving.
An additional point in common in processes (ii) to (v) is that the localization of the organic material thereon is based on a physical displacement of the molecules to be grafted, which is guided as much as possible. The intrinsic resolution of the process is then linked to the control of the method for displacing the molecules: resolution of the mask for (ii), lateral resolution of the mechanical displacements of micronozzles for (iii), protocol for placing under potential to counteract the effects of local diffusion and of broadening of the spots in (iv), etc.
The published patent application EP-A1-0 774 662 (1996) describes the production of a topology for addressing conductive individual plots on a semiconductive surface, which is not the subject of the present invention, since it is assumed that the paving exists, and that it is precisely on this paving that functionalizations are produced. Said patent application mentions its possible use for the local production of electrochemical reactions. As for process (i), this involves a means for locally obtaining an agent for triggering reactions, in this case electrochemical reactions, by selective polarization of an area of the paving, but the complexity of the localization method and of the triggering agent amount to the complexity of producing the paving: it is the paving itself that is supposed to ensure the localization. However, said patent application does not mention specific electrochemical reactions or localized functionalizations. It is thus also a process in which the localization may be obtained by selecting the polarized area, by multiplexing, the support assembly, comprising all the contactable areas, being dipped in the electrochemical bath. In the patents related to process (iii)3, it is mentioned, however, that this method of individual addressing with multiplexing is an impediment to the application on dense etchings, due to the complexity and furthermore the multiplexing.
The current lateral resolution of organic deposits obtained by processes (i)-(iv) is of the order of a few tens to about a hundred microns. This barrier is found everywhere, for various reasons: focussing and chemical stability in the area of grafting for (i), precision of the masking effects for (ii), control of the mechanical displacements of the large-scale high-resolution nozzles for (iii), diffusion and broadening of the plots in the gel, during migration, for (iv). The process of localized addressing by multiplexing appears in principle to be limited only by the current resolution of microelectronics (i.e. a few tenths of a micrometer), but no functionalization process associated with this addressing has been described, to our knowledge. The technique of microcontact printing5 (v) has a resolution of the order of 100 nm on a flat surface. It is not described on a surface structured with paving.
The information regarding the stability of the graft delivering the primary functionalization obtained by processes (i)-(iv) is not all available. However, it may be noted that process (iii), which uses the growth of conductive polymers, does not allow a solid graft on the surface. As is recalled hereinbelow, the electropolymerization of monomers that are precursors of conductive polymers is a mechanism in which the growth of the polymer takes place in solution, and is followed by precipitation of the polymer on the surface: this precipitation generally does not give rise to interface chemical bonds, and delivers functionalization on the surface, but not functionalization of the surface. The process described in the reference in point (v) (WO-A-96 29629) involves an Au—S covalent bond, but which is not obtained on preexisting paving, and which is found to be weaker than the bonds manufactured by the present process.
In summary, the processes of the prior art have the following drawbacks:                since the masking phase conventionally used to perform organic grafting onto a mineral surface is responsible for the localization obtained, the spatial resolution of the graft is that of the masking process. It is thus at best of the order of the current resolutions of microelectronics. Moreover, the localization of the organic material is based on a physical displacement of the molecules to be grafted, which is guided as much as possible. The intrinsic resolution of the process is thus also linked to controlling the field of displacement of the molecules;        several operating steps are necessary: most of the known methods which pursue the same objective proceed via masking; via preliminary, geographically selective physical displacement of molecules, or physicochemical activation which is intrinsically localized, but independent of the resolution of the paving, and then finally by grafting;        the metal-molecule bonds manufactured are found to be relatively weak.        